This invention relates to a key switch as an example of safety switch that may be used, for example, as a door lock switch.
A door lock switch is generally for the purpose of detecting the open or closed condition of a door to a work area containing an automated fabrication machine, serving to switch on and off the power to the machine and locking the door such that it will not open when the machine is in operation.
Such a door lock switch is usually structured such that an operating key provided to the door becomes inserted to a key switch at the entrance as the door is closed, a cam member becoming rotated by the inserted key to switch on a switching part contained within the key switch. When this door is to be opened while the machine is in operation, an operation for stopping the machine is first carried out at an external operating part such that the operating key is pulled out as the door is opened and the cam member is rotated such that the switching part is switched off to disconnect the power supply.
In the above, the cam member is usually structured so as to be at a normal initial position by locking means when the operating key is pulled out such that it cannot be rotated unless its dedicated operating key is employed or easily switched to a switched-on condition by means of an ordinary tool.
FIGS. 17 and 18 show an operating part 77 of a prior art key switch of this type (such as shown in Japanese Patent Publication Tokkai 2002-140962), provided with a pair of intermediate members 71 on both sides of a driver cam 70 so as to be rotatable coaxially therewith. A pair of locking members 72 is provided so as to contact and thereby engage with engaging parts 70a on outer peripheral surfaces of the driver cam 70. As an actuator 73 is advanced and the intermediate members 71 rotate around an rotary shaft 74 against the biasing force of a torsion spring 73, the locking members 72 are moved outward from each other against the biasing force of a coil spring 75 such that the driver cam 70 is released from the engaged condition with the locking members 72 and becomes rotatable. This also causes an operating rod 76 to protrude upward (with reference to the figure) by means of a return spring (not shown) and to open each of normally closed contact points to supply power to a machine to bring it into an operable condition. Although there is an attempt to reduce the overall thickness, the operating part 77 thus structured has many components and is complicated such that its production cost is disadvantageously high.
FIGS. 19-21 show an operating part of another prior art key switch, provided with a driver cam 80 having head lock grooves 81 on both sides, a pair of head lock members 82 having locking parts 83 and a pair of coil springs 84. The driver cam 80 is rotatably supported by a base structure (not shown) through a supporting shaft 85. The head lock members 82 are provided on both sides of the driver cam 80, supported by the supporting shaft 85 so as to be movable reciprocatingly in the direction of the driver cam 80 and pressed towards the driver cam 80 by the force of the coil springs 84 so as to disengageably engage the locking parts 83 with the head lock grooves 81 and to thereby keep the driver cam 80 at its initial rotary position.
As an operating key (not shown) is inserted into the operating part, the tip of this operating key is contacted to the inner surface of the head lock members 82 so as to move both head lock members 82 against the force of the spring, disengaging the locking parts 83 from the head lock grooves 81 to thereby release the driver cam 80 from its locked condition and to leave the driver cam 80 in a rotatable condition. At the same time, an operating rod 86 is moved downward (with reference to FIG. 19) by means of a returning spring (not shown) so as to open each of normally closed contact points to supply power to a machine to bring it into an operable condition.
With an operating part thus structured, the number of components can be reduced but its transverse dimension in the direction of the width tends to be large because the head lock members 82 and the coil springs 85 are arranged in the direction of its width. Moreover, since the opening (not shown) for inserting the operating key remains open all the time, foreign objects such as dust particles are likely to enter therethrough between the driver cam 80 and the head lock members 82. This may have the undesirable effect of preventing the head lock members 82 from effectively locking the driver cam 80, enabling an ordinary tool other than the dedicated actuator, such as a screw driver, inserted into the opening to rotate the driver cam 80 and to activate the switch part.